Charged Polymers for Ethanol Dehydration

ABSTRACT

The systems and methods described herein provide for modified lignins and other compositions that may be useful as entrainers. In embodiments, they may be useful for dehydrating ethanol so that it can be used as an energy source.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/843,815, filed on Sep. 12, 2006. The entire teachings of the aboveapplication are incorporated herein by reference.

FIELD OF APPLICATION

This application relates generally to surfactant compositions useful forproduction of fuel-grade ethanol.

BACKGROUND

As world-wide energy needs continue to grow, there is concern thatdemand for energy may outstrip its supply. Alternative fuel technologiesare desirable to reduce economic dependency on petroleum-based fuels. Asan example, anhydrous ethanol (99.5 vol. % ethanol) may be combined withgasoline for use in internal combustion engines, thereby decreasing theamount of petroleum-based fuel that automobiles consume.

Currently, automobile engines can run efficiently with gasoline mixturescontaining up to 20% anhydrous ethanol, and many states have mandatedthat automobile fuel contain a certain percentage of anhydrous ethanol,typically 5-10%. With engine modifications, anhydrous ethanol may beused alone to fuel vehicles. Although production and blending of ethanolwith gasoline have been used throughout the world for several decades,use of these technologies has been limited by the high costs ofproducing anhydrous alcohol.

Ethanol is typically produced by fermentation of biomass material anddistillation to form a single liquid phase containing approximatelyequal volumes of ethanol and water. The EtOH/water mixture may then beseparated using chemicals like cyclohexane to yield an anhydrous alcoholphase, which may contain minor amounts of other alcohols, such aspropanol or butanol. Adsorption and solvent extraction are alternativeor supplemental methods of separating alcohol and water.

Ethanol distillation techniques and their modifications produce 95% byweight ethanol solutions efficiently. However, concentrating an ethanolsolution beyond 96.4% by weight has been difficult. At approximatelythis concentration, equilibrium is reached between the liquid and thevapor phases, where both phases have the same concentration of ethanoland water. This solution in equilibrium is called an azeotrope, or aconstant-boiling mixture. For ethanol, a binary, minimum-boilingazeotrope is formed.

To dehydrate an ethanol solution beyond the 96.5% concentration, one oftwo main procedures may be employed. One procedure involves azeotropicdistillation. This method has been used for decades as a means forpurification of chemicals from azeotropic mixtures. The distillationprocedure involves adding a third chemical called an entrainer to thesystem. This third component interacts with both of the water andethanol to create a ternary azeotrope which is stronger than theoriginal binary azeotrope. A typical ternary phase separation isachieved through the use of benzene as an entrainer. This system yieldsthree distinct regions on the column that represent differentcompositions. The uppermost region yields anhydrous ethanol.

As an alternative procedure for dehydrating ethanol beyond the 96.5%concentration, molecular sieves may be used for the dehydration step.Molecular sieves include zeolites, which are highly orderedaluminosilicates having very precise pore sizes. They are produced assmall beads or pellets. The pore structure is capable of performing sizeexclusion on the molecular level. Ethanol is on the order of4.4Angstroms and water is approximately 2.8 Angstroms. Molecular sievesselected with a pore size of3.0 Angstroms can therefore be used toseparate the water from the ethanol via size differences. To use thisdehydration method, the azeotropic stream of vaporized alcohol and wateris passed through a vessel containing the molecular sieves. The water isthen adsorbed into the pores and the larger ethanol passes by and iscondensed into tanks. Since the water adsorption occurs via a surfacephenomenon, the particles can be regenerated for reuse by drying withheat or by vacuum. While this system is efficient and does not impartchemical contamination, it does require the use of expensive zeolites.

While a variety of techniques exist for dehydrating the water-ethanolazeotrope, none are cheap or efficient, and all have significantdrawbacks. There remains a need in the art for efficient andcost-effective systems and methods to facilitate ethanol dehydration, sothat anhydrous ethanol may become more readily available for energyproduction.

SUMMARY

The invention relates to novel materials and methods useful indehydrating ethanol. In embodiments, the invention relates to methodsfor dehydrating an ethanol solution comprising distilling the ethanolsolution in the presence of a molecular sieve characterized by a porouscore and a water-permeable polymeric coating impermeable to ethanol. Inparticular, the molecular sieve can be characterized by a high chargedensity. This can be achieved by using a porous core comprises apolyanionic polymer. In embodiments, the coating comprises apolycationic polymer or nonionic polymer, either of which can beoptionally crosslinked. Alternatively, the porous core comprises apolycationic polymer. In embodiments, the coating comprises apolyanionic polymer or nonionic polymer, either rof which can beoptionally crosslinked.

The invention also relates to molecular sieves characterized by a porouscore and a water-permeable polymeric coating impermeable to ethanol, themolecular sieves being those described above.

In embodiments, the invention relates to a method for dehydrating anethanol solution comprising distilling the ethanol solution in thepresence of an entrainer comprising a lignin or lignin derivative. Thelignin or lignin derivative can be solid in ethanol. The entrainer canbe a carboxylated lignin, such as can be produced by reacting a ligninwith an anhydride, including a succinic anhydride or alkylated succinicanhydride. The lignin can also be a kraft lignin characterized byhydroxyl groups. In embodiments, between about 50 and 100% of thehydroxyl groups of the lignin are functionalized. In addition, oralternatively, the entrainer is further characterized by a hydrophilicpolymer substituent, such as a polyethylene oxide and a polypropyleneoxide.

DESCRIPTION

In other embodiments useful for ethanol dehydration, particles may beformed from highly charged (hence hydrophilic) polyelectrolyte cores andan alcohol-insoluble skin to create an organic analog of a molecularsieve. While it is known in the art that high charge density coatingsare capable of dehydrating ethanol via permvaporation methodologies (seeToutianoush, and Tieke Materials Science and Engineering C 22 (2002)459-463), a similar method might be efficiently utilized without the useof energy intensive distillative process. For example, a selectivelyadsorbent particle may be used in a typical filtration manner to removeresidual water and produce dehydrated ethanol in accordance with thesystems and methods disclosed herein.

In embodiments, water may be absorbed onto such a particle, and ethanolmay be excluded. In one embodiment, the particle may comprise apolyanion core material, and the exterior may be covered with apolycation that creates a complex at the interface and an insoluble skinwith a high crosslink density (either electrostatic or physicalcrosslinks) that excludes ethanol from the particle interior. In otherembodiments, the coating around a polyanion core could consist of anonionic material that is insoluble in ethanol. Polyanions are not theonly particles that can be used as the high charge density material. Inembodiments, a polycationic material could be used as the core materialtreated with either a polyanion or nonionic polymer coating. In anotherembodiment, a nonionic, water soluble core material can be coated withanother material, either nonionic, cationic, or anionic.

Not to be bound by theory, the systems and methods disclosed herein mayhave in common a water soluble core with some type of passivatingcoating on the surface, whereby the coating maintains water within thecore.

In embodiments, the exterior coating may be oppositely charged from thatof the core. The coating polyelectrolyte may condense upon the corecreating three “zones”, one anionic, one cationic, and a middle phase.The resulting middle phase, consisting of tight ion pairs due to theelectrostatic charge attraction, is a passivated, area between the twooppositely charged regions (the core and the surface). Using this middlezone as a semipermeable membrane, water may be preferably kept withinthe core, with minimal flux back into the ethanol environment.

As an exemplary embodiment, a particle may be formed using a substancesuch as encapsulated Carbopol, which is a crosslinked polyacrylic acid.A protective skin may be formable on such a particle using a polycationsuch as chitosan to complex the cationic charges on the surface. Inembodiments, the desired particle may be formed with layering to controlits porosity. In another embodiment, a micron sized particles such asCarbopol may be surrounded by polycationic polymers such as branched orlinear polyethyleneimine with molecular weights between 2000 and 100,000gmol⁻¹. Oligomeric entities may also be usable to create the layeredcore-shell morphology. Mixing the particles into an anhydrous solutionof polycation may form a coating on the surface of the particle uponintroduction. The coating may be less than 100 nm in thickness forincreased transport properties across the coating. In embodiments,naturally occurring polysaccharide multi-carboxylates could also be usedto form the exterior complex, for example materials such as pectin andcarboxymethylcellulose. In these illustrative embodiments, the charge onthe core particle may be varied to alter the thickness of the coating.

In other embodiments, particles may be formed comprising aninorganic-organic hybrid. For example, the core may be formed with aninexpensive porous silicate or other naturally occurring or syntheticdesiccant. In embodiments, the porous substrate may first be loaded withsalts that would be effective in absorbing water, for example potassiumcarbonate, before encapsulating the assembly with a skin formed in situ.In embodiments, the skin may be a charge-charge complex (a tightmolecular network) to exclude alcohol from penetrating into the core.For example, chitosan can be deposited spontaneously on silica, thencomplexed with a polyanion. A composite such as this would allow waterabsorption and ethanol exclusion to be separately performed by the coreand skin of such engineered particles. In embodiments, to concentrateethanol using such particles, they may be added to hydrated alcohol inan appropriate amount so that water may be absorbed onto the particlesand dehydrated effluent alcohol may be collected for use as a fueladditive. The water-containing particles may be dried out and reused,thus enhancing the efficiency of the process.

Disclosed herein are systems and methods useful in energy applications,with particular applicability to the dehydration of azeotropic ethanolsolutions. In embodiments, the systems and methods described herein mayinvolve the use of modified lignins and formulations thereof. Lignin isa naturally-occurring cross-linked, polymerized macromolecule comprisedof aliphatic and aromatic portions with alcohol functionalityinterspersed. Lignin polymers incorporate three monolignol monomers,methoxylated to various degrees: p-coumaryl alcohol, coniferyl alcohol,and sinapyl alcohol. These are incorporated into lignin in the form ofthe phenylpropanoids, p-hydroxyphenyl, guaiacyl, and syringalrespectively. The systems and methods disclosed herein describe hownaturally-occurring (i.e., native) and unnatural or modified lignin maybe modified through functionalization of the resident alcohol moietiesto alter the properties of the polymer. Such a functionalized lignin maybe termed a “modified lignin.” The word “lignin”, as used herein isintended to include natural and non-natural lignins which possess aplurality of lignin monomers and is intended to embrace lignin, kraftlignin, lignin isolated from bagasse and pulp, oxidized lignin,alkylated lignin, demethoxylated lignin, lignin oligomers, and the like.

Lignin and oxidized lignin are waste products from the paper industry.Oxidized lignin is characterized by a plurality of hydroxyl groups whichcan be conveniently reacted. Oxidized lignin is described, for example,in U.S. Pat. No. 4,790,382 and is characterized by a plurality ofhydroxyl groups which can be conveniently reacted. Similarly, kraftlignins, such as indulins, including Indulin AT, can be used. Forexample, the hydroxyl groups can be reacted with succinic anhydride andsimilar compounds to form a carboxylic acid-substituted lignin, by aring opening reaction. The systems and methods disclosed herein describehow naturally-occurring (i.e., native) lignin may be modified throughfunctionalization of the resident alcohol moieties to alter theproperties of the polymer. Such a functionalized lignin may be termed amodified lignin.

In embodiments, adding a reactive agent such as succinic anhydride oralkylated succinic anhydride to a native lignin may produce a modifiedlignin of the invention. Alkylated succinic anhydride is commonly usedin the paper industry as a sizing agent. The alkyl additions are longchain hydrocarbons typically containing 16-18 carbon atoms. However,alkylated succinic acids having alkyl side chains having more than 1carbon atom, such as 1 to 30 carbon atoms can be used as well. Suchalkyl groups are defined herein to include straight chain, branchedcahain or cyclized alkyls as well as saturated and unsaturated alkyls.Examples of alkylated succinic anhydride include EKA ASA 200® (a mixtureof C16 and C18 ASA) and EKA ASA 210® (a C18 ASA). Addition of ananhydride, such as a succinic anhydride or alkylated succinic anhydrideto the resident alcohol groups result in new ester linkages and theformation of carboxylic acids via a ring opening mechanism. Addition ofanhydride to the resident alcohol groups result in new ester linkagesand/or the formation of carboxylic acids via a ring opening mechanism.With the newly added carboxylic acid functionality, the lignin becomesmore water soluble.

In other embodiments, the hydroxyl group can be reacted with adicarboxylic acid, such as maleic acid, or activated esters oranhydrides thereof to form a carboxylic acid substituted lignin. Forexample, the anhydride derived from many acids can be utilized, such asadipic acid, or the functionality can be derived from natural compoundssuch as a polysaccharide that contains carboxylic acid groups.Non-limiting examples include pectin or alginate, and the like, andsynthesized polymers such as polyacrylic or methacrylic acid homo orco-polymers. Further, activated esters can be used in place of theanhydride. Other examples will be apparent to those of ordinary skill inthe art. The degree of functionalization (i.e., the percentage ofhydroxyl groups that are reacted to present an ionic moiety) can bebetween 20% and 80%, preferably between 50% and 80%.

In other embodiments, lignin (oxidized or native) may be treated bychemically reacting it with reagents to tune the hydrophilicity topresent alcohol groups. Examples of such reagents include hydrophilicmolecules, or hydrophilic polymers, such as poly(ethylene glycol) (PEG)or poly(propylene glycol) (PPO) and combinations thereof. In a preferredembodiment, the hydrophilic polymer can have a molecular weight between700 and 2500 g/mol Addition of PEG or PPO (with or withoutacidification) can be useful in stabilization of the product in saltsolutions, particularly divalent cation salts. In this embodiment, theamount of polymer to lignin is preferably added in an amount between 25%and 75%.

As described above, ethanol is naturally hydrated when it is fermentedand must be dehydrated and purified prior to its use as a fuel. Inembodiments, a modified lignin base may be formed to create a branchedor networked polymer with functional groups that form hydrogen bonds todisrupt the inherent water-ethanol azeotrope during distillation. Inembodiments, the dehydration of ethanol may be accomplished by usingparticles designed to absorb water while excluding ethanol by utilizinga molecularly designed architecture on a porous substrate, for example,or by creating a layered substrate with a water soluble/swellable corewith a charge complex exterior shell to exclude ethanol whilepreferentially absorbing water.

For the dehydration of ethanol, oxidized lignin may be used withoutfurther modification, or it may be oxidized further to create a largelybranched molecule with a high molecular weight and a large number ofalcohol groups of various types (primary, secondary, tertiary andbenzylic). Using lignin by itself to act as a solid entrainer added tothe distillation apparatus may be possible due to the alcoholfunctionalities. These functionalities are expected to change thethermodynamic equilibrium enough to create a different azeotropiccomposition, preferably more than the standard azeotrope at 96.4% byweight. By adding modified or unmodified lignin to an ethanol-watermixture followed by distillation, the resulting distillate may be morepure than the feed.

The solid entrainers of the invention are not removed with the ethanolduring distillation and, accordingly, can be readily removed andoptionally recycled.

EXAMPLE 1

Indulin AT is used as the lignin source. Indulin AT is a purified formof the lignin obtained from the black liquor in the Kraft pulpingprocess. Here, Indulin AT (5.0 g) is suspended in 150 ml of acetone.Alkyl succinic anhydride in the form of Eka SA 210 (25.0 g) is added tothe suspension. The reaction is performed in a bomb and heated to 70° C.over the course of 48 hours.

EXAMPLE 2

Indulin AT (5.0 g) is mixed with 10.0 g Eka SA 210 in a bomb filled with150 ml of acetone. The mixture is heated to 70° C. over 48 hours, andthe product is recovered.

EXAMPLE 3

Indulin AT (5.0 g) is mixed with 5.0 g Eka SA 210 in a bomb filled withacetone. The mixture is heated to 70° C. over 48 hours. The resultingmixture is filtered; the supernatant is recovered and diluted withalkaline water and dried.

EXAMPLE 4

Indulin AT (5.0 g) is mixed with 4.0 g Eka SA 210 in a bomb filled with150 ml of acetone. The mixture is heated to 70° C. over 48 hours. Theresulting mixture is filtered; the supernatant is recovered, dilutedwith alkaline water and dried.

EXAMPLE 5

Indulin AT (5.0 g) is mixed with3.0 g Eka SA 210 in a bomb filled with150 ml of acetone. The mixture is heated to 70° C. over 48 hours. Theresulting mixture is filtered; the supernatant is recovered, dilutedwith alkaline water and dried.

EXAMPLE 6

Indulin AT (5.0 g) is mixed with 2.5 g Eka SA 210 in a bomb filled with150 ml of acetone. The mixture is heated to 70° C. over 48 hours. Theresulting mixture is filtered; the supernatant is recovered, dilutedwith alkaline water and dried.

EXAMPLE 7

Indulin AT (5.0 g) is mixed with 1.0 g Eka SA 210 and3.0 g succinicanhydride in a bomb filled with 150 ml of acetone. The mixture is heatedto 70° C. over 48 hours. The resulting mixture is filtered; thesupernatant is recovered, diluted with alkaline water and dried.

EXAMPLE 8

Indulin AT (5.0 g) is mixed with 2.0 g Eka SA 210 and 2.0 g succinicanhydride in a bomb filled with 150 ml of acetone. The mixture is heatedto 70° C. over 48 hours. The resulting mixture is filtered; thesupernatant is recovered, diluted with alkaline water and dried.

EXAMPLE 9

Indulin AT (5.0 g) is mixed with3.0 g Eka SA 210 and 1.0 g succinicanhydride in a bomb filled with 150 ml of acetone. The mixture is heatedto 70° C. over 48 hours. The resulting mixture is filtered; thesupernatant is recovered, diluted with alkaline water and dried.

EXAMPLE 10

Indulin AT (5.0 g) is mixed with 4.0 g Eka SA 210 and 1.0 g polyethyleneglycol diglycidyl ether in a bomb filled with 150 ml of acetone. Themixture is heated to 70° C. over 48 hours. The resulting mixture isfiltered; the supernatant is recovered, diluted with alkaline water anddried.

EXAMPLE 11

Indulin AT (5.0 g) is mixed with3.0 g Eka SA 210 and 1.0 g polypropyleneoxide diglycidyl ether in a bomb filled with 150 ml of acetone. Themixture is heated to 70° C. over 48 hours. The resulting mixture isfiltered; the supernatant is recovered, diluted with alkaline water anddried.

EQUIVALENTS

While specific embodiments of the subject invention have been discussed,the above specification is illustrative and not restrictive. Manyvariations of the invention will become apparent to those skilled in theart upon review of this specification. The full scope of the inventionshould be determined by reference to the claims, along with their fullscope of equivalents, and the specification, along with such variations.

Unless otherwise indicated, all numbers expressing quantities ofingredients, reaction conditions, and so forth used in the specificationand claims are to be understood as being modified in all instances bythe term “about.” Accordingly, unless indicated to the contrary, thenumerical parameters set forth in this specification and attached claimsare approximations that may vary depending upon the desired propertiessought to be obtained by the present invention.

1. A method for dehydrating an ethanol solution comprising distillingthe ethanol solution in the presence of a molecular sieve characterizedby a porous core and a water-permeable polymeric coating impermeable toethanol.
 2. The method in accordance with claim 1 wherein the surface ofthe molecular sieve is characterized by a high charge density.
 3. Themethod in accordance with claim 2 wherein the coating has a thickness ofless than about 100 nm.
 4. The method in accordance with claim 2 whereinthe coating comprises pores having a mean diameter less than 4Angstroms.
 5. The method in accordance with claim 1 wherein the porouscore comprises silica or a polyanionic polymer.
 6. The method inaccordance with claim 5 wherein the coating comprises a polycationicpolymer.
 7. The method in accordance with claim 6 wherein thepolycationic polymer is crosslinked.
 8. The method in accordance withclaim 6 further comprising an additional coating comprising apolyanionic polymer.
 9. The method in accordance with claim 3 whereinthe coating comprises a nonionic polymer.
 10. The method in accordancewith claim 1 wherein the porous core comprises a polycationic polymer.11. The method in accordance with claim 10 wherein the coating comprisesa polyanionic polymer.
 12. The method in accordance with claim 11wherein the polyanionic polymer is crosslinked.
 13. The method inaccordance with claim 11 further comprising an additional coatingcomprising a polycationic polymer.
 14. The method in accordance withclaim 10 wherein the coating comprises a nonionic polymer.
 15. Amolecular sieve characterized by a porous core and a water-permeablepolymeric coating impermeable to ethanol.
 16. The molecular sieve inaccordance with claim 15 comprising the porous core comprises apolyanionic polymer.
 17. The molecular sieve in accordance with claim 16wherein the coating comprises a polycationic polymer.
 18. The molecularsieve in accordance with claim 17 wherein the polycationic polymer thecoating has a thickness of less than about 100 nm.
 19. The molecularsieve in accordance with claim 15 comprising the porous core comprises apolycationic polymer.
 20. The molecular sieve in accordance with claim19 wherein the coating comprises a polyanionic polymer.
 21. Themolecular sieve in accordance with claim 20 wherein the polyanionicpolymer the coating has a thickness of less than about 100 nm.
 22. Amethod for dehydrating an ethanol solution comprising distilling theethanol solution in the presence of an entrainer comprising a lignin orlignin derivative.
 23. The method in accordance with claim 22 whereinthe entrainer is a carboxylated lignin.
 24. The method in accordancewith claim 22 wherein the entrainer is produced by reacting a ligninwith an anhydride.
 25. The method in accordance with claim 24 whereinthe anhydride is a succinic anhydride.
 26. The method in accordance withclaim 24 wherein the anhydride is an alkylated succinic anhydride. 27.The method in accordance with claim 22 wherein the lignin is a kraftlignin characterized by hydroxyl groups.
 28. The method in accordancewith claim 27 wherein between about 50 and 100% of the hydroxyl groupsare functionalized.
 29. The method in accordance with claim 22 whereinthe entrainer is a solid.
 30. The method in accordance with claim 23wherein the entrainer is further characterized by a hydrophilic polymersubstituent.
 31. The method in accordance with claim 30 wherein thehydrophilic polymer substituent is selected from the group consisting ofa polyethylene oxide and a polypropylene oxide.
 32. The method inaccordance with claim 31 wherein the hydrophilic polymer substituent isselected from the group consisting of a polyethylene oxide diglycidylether and a polypropylene oxide diglycidyl ether.
 33. The method inaccordance with claim 32 wherein the hydrophilic polymer substituent hasa molecular weight between about 700 and 2500 g/mol.